The present invention relates to a clutch control method and a clutch controller for a motor-driven power steering apparatus and, more particularly, to a clutch control method to be performed when mechanical rotation of a motor is disabled after a power steering apparatus is activated and a clutch controller which can detect abnormality of a clutch driver.
A power steering apparatus for assisting a steering force of a steering wheel by a motor is conventionally known.
FIG. 5 is a view showing an arrangement of a conventional motor-driven power steering apparatus, and FIG. 6 is a block diagram of the same.
Referring to FIG. 5, reference numeral 1 denotes a signal controller; 2, an ignition switch; 3, an engine; 4, a generator driven by the engine 3; 4a, an L terminal of the generator 4; 5, a battery; 6, a torque sensor for detecting a steering torque obtained by a steering wheel 33 and its steering direction; 7, a steering angle sensor for detecting a steering angle and an angular speed of a steering mechanism 34 for pivoting wheels; 8, a motor for assisting a steering force; and 9, an electromagnetic clutch. The electromagnetic clutch 9 flows or shuts off a current with respect to a clutch coil to perform a clutch operation, thereby connecting or disconnecting a torque of the motor 8 to or from the steering mechanism 34. Reference numeral 30 denotes a power controller.
Referring to FIG. 6, reference numeral 10 denotes a warning lamp (power steering warning lamp); 11, a signal processor; 12, a vehicle speed pulse input unit; 13, an L terminal voltage detector for detecting a voltage of the L terminal 4a of the generator 4; 14, a torque voltage input unit; 15, a steering angle/angular speed input unit; 16, an A/D converter; 17, a clutch driver for driving the electromagnetic clutch 9; 18, a lamp driver for driving the power steering warning lamp 10; 19, a power source; 20, a reckless driving detector; 21, a PWM output unit; 22, a direction switch; 31, a motor driver; 32, a current sensor.
Referring FIGS. 5 and 6, the motor 8 and the electromagnetic clutch 9 are related to the present invention. The motor 8 is driven by the motor driver 31 under the control of a PWM value signal and a direction signal supplied from the PWM output unit 21 and the direction switch 22, respectively, which receive designation from the signal processor 11. The electromagnetic clutch 9 is driven by the clutch driver 17 which receives designation from the signal processor 11.
FIG. 7 is a circuit diagram showing the conventional clutch driver 17. Referring to FIG. 7, reference symbols T1 and T2 denote the output and input terminals, respectively, of the signal processor 11; Q1 to Q4, transistors; CP, a comparator; 9a, a clutch coil; and E, an earth.
In this arrangement, when a signal of level "L" is output from the terminal T1, the transistors Q1, Q2, and Q3 are turned on to flow a current through the clutch coil 9a. When a signal of level "H" is output from the terminal T1, the transistors Q1, Q2, and Q3 are turned off to shut off the current from the clutch coil 9a. An emitter potential of the transistor Q3 is normally at 0.24 V. In this case, a signal output from the comparator CP to the terminal T2 is at level "L" to indicate a normal operation.
If, however, an overcurrent is flowed to the transistor Q3 for a certain reason, V.sub.CE of the transistor Q3 is increased, and an input voltage to the inverting terminal of the comparator CP is decreased to be smaller than 0.24 V. Therefore, the comparator CP outputs a signal of level "H" to inform the signal processor 11 of the abnormality of the clutch driver 17 side. In addition, if the clutch coil 9a is disconnected or a ground line (a line at the collector side of the transistor Q3) and the earth are shortcircuited, the input voltage to the inverting terminal of the comparator CP is similarly decreased. Therefore, the comparator CP outputs a signal of level "H" to inform the signal processor 11 of the abnormality.
If, however, mechanical rotation of the motor for assisting the steering force is disabled due to, e.g., removal of a field magnet, steering of an automobile is disabled to expose a driver to a serious danger.
In addition, in the clutch driver described above, even if an overcurrent caused by rare short of the clutch coil 9a is detected, a countermeasure of, e.g., disconnecting the electromagnet clutch 9 cannot be performed. Therefore, since the electromagnetic clutch 9 cannot be disconnected in case of emergency, a driver is exposed to a serious danger.